Apparatus for desynchronizing



Sept. 27, 1960 R. B. FOLLANSBEE APPARATUS FOR nssyucuaomzms Filed Feb. 23, 1955 Q. as

IN VEN TOR.

ROBERT B. FOLLANSBEE H/ S ATTORNEYS United States Patent APPARATUS FOR DESYNCHRONIZING Robert B. Follansbee, South Portland, Maine, assigpor to Portland Pipe Line Corporation, Portland, Mame, a corporation of Maine Filed Feb. 23, 1955, Ser. No. 489,943

2 Claims. (Cl. 318-85) This invention relates to apparatus for pumping incompressible fluids and more particularly, to a system employing plural pumps for distributing fluids such as water and oil from a main pumping station to distributor lines in inhabited areas. More specifically, the invention relates to a novel system and apparatus for pumping fluids in such manner that vibration caused by fluid surges, cavitation, etc, is largely obviated.

As will be readily understood by those skilled in the art, it has long been the practice to employ a plurality of dcubleacting pumps, and more particularly, a specific type pump known as a triplex pump, for distributing liquids such as oil and water from a central storage chamber to a distributor line manifolding the outlet from the plural pumps for delivery to individual outlet lines. Ccnventicnally, such type pumping arrangements are installed in inhabited or urban areas, and in practice it frequently occurs that an unusually strong vibration is set up in the pumping equipment, distributor lines and adjacent earth, all leading to disturbances in the surrounding hab'ita-tions. Attempts have been made toalleviate this difficulty by equipping the pumps with suction air bottles and/ or with nitrogen bag-type (Greer) accumulators. These devices have been intended to act as surge dampeners to smooth the flow of the liquid through the discharge line in order to reduce pulsations and the tendency to induce vibrations in the surrounding earth work. Such efforts, however, have failed to wholly eliminate the trouble. Other unsuccessful attempts to eliminate these strong vibrations have taken the form of employing an equalizer line which is adapted to be connected to the discharge side of each pump whereby manipulation of a control valve in the connection between any two or more pumps modulates the fluid flow.

Investigation of the problem directed to ascertaining whether the excessively strong vibrations were due to a deficiency in the pump, such. as a lack of proper filling, possible cavitation in the suction line, and/ or location of the by-pass valve return unit, led to the discovery that the difficulty was definitely related to the synchronous operation of two or more pumps, which condition is unpredictable and occurs by mere chance.

Accordingly, 'the present invention is directed to a novel and improved system incorporating an arrangement whereby the plural pumps of a given installation can be operated in a predetermined desynchronized fashion in such manner as to remain locked in this condition. The novel pumping system of the invention may be briefly described as comprising a plurality of double-acting triplex pumps, ie a known type pump incorporating a single driving element which is adapted to actuate three double-acting pumping chambers with a predetermined phase differential, a synchronous electric motor connected to drive each such pump, and a control arrangement for the motors so arranged as to be adapted to selectively vary the phase relationship between any of the plural pumps and to lock the pumps in a desired desynchronized condition. A feature of the invention is the ICC novel innovation in the control circuit for the respective synchronous motors which is so arranged as to employ the electrical characteristic of a synchronous motor to desynchronize each such motor with respect to the other motors of a given installation. Another feature of the invention resides in the employment of a stroboscopic scanning device for continuously visually indicating the respective phase relationships between the motors and pumps of the system.

It is therefore an object of the invention to provide an improved fluid pump arrangement for distributing incompressible fluids without inducing strong vibrations in adpacent structures. It is a further object of the invention to provide an improved fluid pumping system having means for readily imparting a predetermined phase differential between plural pumps of the system. A still further object of the invention is the provision of an improved synchronous motor drive arrangement for plural driven elements. Another object of the invention is the provision of a novel visual indicator structure for displaying a synchronous and/or desynohronized condition between plural rotating elements. A further object of the invention is the provision of an improved control mechanism for shifting the phase relationship be tween plural driven elements actuated by parallel synchronous electric motors. Other and distinct objects of the invention will become apparent from the description and claims which follow.

The invention will be better understood by reference to the accompanying drawings in which:

Fig. l is a schematic view, partly in perspective of the pumping system according to the invention; and

Fig. 2 is a perspective view of the stroboscopic control arrangement of the invention.

Referring to Fig. 1, it will be seen that the invention comprises driven elements, for example, a pumping system employing four independent triplex pumps 10, 5t), and 130, respectively, each of the pumps having three double-acting pumping chambers (not shown), as is well known in the art. Actuator rods 11, 12 and 13 project laterally from the casing of pump 10 and are respectively adapted to actuate the pistons (not shown) in individual pumping chambers. Similar rods project from each of the pumps 50, 90 and 130, but in view of the fact that the structures of the respective. pump and drive arrangements are identical, the description herein will be confined to a detailed discussion of the drive arrangement for pump 10. It thus will be understood that similar reference numerals denote similar structures in the respective units.

Pump rods 11, 12 and 13 are pivotally connected to actuator links 16, 17 and 18 which in turn are pivotally mounted on the respective free ends of crank arms 21, 22 and 23 carried on a rotatable shaft 25. Shaft 25 is journalled for rotation in a manner (not illustrated) well known in the art and fixedly carries a driven gear 26. Gear 26 meshes with a driving pinion 27 carried on the end of a motor shaft 28 adapted to be driven by a synchronous motor .30 designated by a circle the principal components of which are stationary A.C. armature windings 30a and rotating D.C. field windings 31. It thus will be understood that operation of motor 30 will rotate shaft 28 and pinion 27 to turn gear 26 and therewith shaft 25 causing crank arms 21, 22 and 23 to actuate the respective pump actuator rods in a predetermined sequence dependent upon the relative phase relationship between the respective crank arms. Identical driving structures are provided for each of the other pumps 50, 90 and 130 which are connected to be driven by similar synchronous electric motors 70, and 150.

The control circuit for each motor is identical and in the interest of clarity only that for motor 30 has been illustrated in detail in the drawings. It will be understood, however, that the following description of the control arrangement for the synchronous motor 30 is applicable to the control circuits connected with the other motors. As shown, motor 30 is connected via electrical leads 29 to a conventional synchronous motor starting unit consisting of closing switch 32, opening switch 32A, resistor 32C, solenoid Winding 33, rod 34, 3 pole switch 35, switch 36, solenoid windings 49 and 49A and choke coil 49C which may be of any of the conventional types well known in the art, the starting unit being in turn connected via wires 44 across a three-phase A.C. power line P which also serves to energize motors 70, 110- and 15% whereby the four motors are connected in parallel. In accordance with the invention, the rotating DC. field wind-ing 31 of the motor is separately energized from a DC. source and includes a normally closed, series switch 32. Switch 32 is adapted to be actuated from a solenoid winding 33 connected across two of the three-phase leads 29 to motor 30. Winding 33, when energized, serves to actuate a control bar 34 to close switch 32 and energize the DC. field winding of the motor. A second series switch 36, having normally closed contacts, is provided in the circuit of winding 33 and is adapted to be actuated by windings 49 and 49A via actuator bar 37 in a known manner to apply DC power to field circuit 31 of the motor 30 at proper speed and phase relationship. Actuator bar 37 can also be operated by a third winding 38 which when energized opens switch 36. Winding 38 in turn is connected in series with a power source by means of a circuit 39 including a normally closed switch 40 and a normally open push-button switch 45. Normal starting of the motor is carried out by closing the 3 pole switch 35, which causes motor to start as an induction motor and further results in inducing an alternating voltage in the field winding 31 at a frequency proportional to the speed of the rotating element on which these field windings are wound. This voltage induced in the field winding 31 causes -a current to flow through the circuit made up of choke coil 49C which is parallelled by winding 49A, resistor 32C and switch 32A. The portion of the current in winding 49A results in holding switch 36 open. As the motor approaches synchronous speed, less current flows through winding 49A due to the decreased impedance of choke coil 49C; and at proper speed and phase angle, both windings 49 and 49A are sufiiciently de-energized to permit rod 37 to be actuated by spring 38A to close contacts 36 thus applying voltage to winding 33. This causes rod 34 to operate closing switch 32 and opening switch 32A, thus applying DC. to field winding 31 and interrupting the field discharge circuit, all in a manner well known in the art as the polarized field frequency relay method of field application.

Switch. 45 is adapted to be selectively, manually actuated to energize winding 38, and is provided with a suitable timer control mechanism, illustrated in the drawing, for example, as a dash pot unit 47 having a. var able throttle valve 48. Energizing winding 38 causes rod 37 to open switch 36, thereby de-energizing winding 33 causing rod 34 to open switch 32 and close switch 32A. This removes D.C. from the field winding for the period of time determined by setting of valve 43 on dash pot unit 47. Upon interruption of power to winding 38 by switch 45, DC is reapplied to field winding 31 at the proper phase angle by operation or" windings 4% and 45 A as occurs in the initial starting operation. The operation of the pushbutton switch will be readily apparent to those skilled in the art and consists in that depression of the switch to energize circuit 39 will also actuate the dash pot unit 47 in such manner as to hold the switch in its closed position for a predetermined length of time, dependent upon thesetting of valve 48, all in a manner well understood in the .art. The normally closed switch 40 is provided with an actuator rod 41 serving as a solenoid core for a solenoid winding 42 connected in series with one line of the three-phase power leads 44. The characteristics of winding 42 are so chosen that switch 40 will normally remain closed unless the current in the three-phase line exceeds a predetermined overload value.

The operation of the above-described control circuitry for the respective synchronous motor driving elements of the system will be better understood from the more detailed description set out infra. However, it will be apparent that its function is to provide selective control over the relative phase-relationships between all of the motors which are connected in parallel on a main threephase power source by selective deenergization of the motor field, it being appreciated that the characteristics of synchronous motors operating in parallel from a single distribution system are such that the motors will remain locked in step independent of variations in loading. Since the control arrangement requires manual supervision, it is necesary that some means be provided to visually indicate the respective phase-relationships between the individual motors. For this purpose, a supervisory circuit including electrical leads 171 is provided with a plurality of parallel switching units A, B, C, and D connected to be operated in synchronized relationship from the respective pumps. The switching units are identical and only unit A will be particularly described. It will be understood, however, that this description is applicable to the remaining units.

Unit A comprises a manual switch 172 and an automatic make and break circuit contactor mechanism 175, the arrangement being such that closing of switch 172 serves to connect unit 175- in series with the source of power via electrical leads 171. Unit 1'75 includes a gear 176 mounted for rotation with pump shaft 2-5 and meshing with a driven pinion member 177, the size of the gearing being so chosen that one revolution of gear 17 6 rotates pinion 177 three times. Pinion 177 fixedly supports a disc-like contact or switch element 178 formed of an electrically insulating material but being provided with a conductive segment 179 which is electrically connected to one of the leads 171 of circuit 176 in a manner well known in the art. Disc 178 is positioned adjacent to a fixed contact element 174 which is connected to the other electrical lead of circuit 171 whereby rotation of disc 178 by the pump shaft 25 serves to periodicaily complete a series circuit each time segment 179 contacts plate 174. Since gear 176 rotates disc 178 three times for each revolution of the pump shaft, it will be appreciated that the disc can be so adjusted in relationship to the physical position of the pump cranks 211, 2:2 and 23 as to close circuit 170 each time a respective pump rod 11, 12 or 13 completes a pumping cycle for each pump chamber. The completion of circuit 171 will coincide with the movement of the three crank elements each element completes the forward stroke of its actuator rod 11, 12 and 13. With this arrangement, it will be understood that circuit 171 is completed three times during a single revolution of shaft 25 to synchronize the pumping action with the operation of the circuit for a purpose hereinafter apparent.

Supervisory circuit 170 in turn is connected to activate a stroboscopic angular phase indicating unit 1% via a pair of electrical lead wires 181 connected across leads 171. Lead wires 181 are electrically connected in series with a high frequency light flasher 180 having a known type stroboscopic lamp. The lead wires 1S2 connect light flasher 180 to one-phase of said three-phase A.C. power line P. Light flasher 1% is also connected to circuit 17% by means of lead wires 18 1. it will be thus understood that each time a make and break unit A, B, C or D completes the circuit 170, the light flasher 180 will be energized to illuminate an adjacent stroboscopic reference mechanism 185. This reference mechanism illustrated generally in Fig. 1 and in greater detail in Fig. 2 comprises a fractional horse-power synchronous motor 136 energized by one-phase of said three-phase A.C. power line P and connected through a gear train (not shown) and disposed with-in a casing 187 to rotate a disc 188 mounted on the front of casing 187 and bearing a single radial line 189 in the path of illumination from flasher unit 180. Motor 186 and gear train within casing 187 are so chosen that disc 188 makes three revolutions for each revolution of the pump crank shaft 25, the characteristics of the synchronous motor 186 serving to lock movement of disc 188 in a substantially invariable synchronized relationship with the pump crank shaft rotation.

, The details of the reference circuit arrangement will be better understood by viewing Fig. 2 illustrating the unit in enlarged diagrammatic form. As shown therein, disc 188, which is connected through gear train within casing 187 to be rotated by the synchronous motor 186, is surrounded by a graduated scale 183 bearing indicia marking equidistant points representing radian displacement. Scale 183 is adapted to cooperate with the single radial line 189 carried by disc 188 in conjunction with the high frequency flasher unit 180 to pictorially portray a visual indication of the relative phase relationship between the several pumps 10, 50, 90 and 130. This will be better understood from the following description of the operation, function and purpose of the instant invention.

When a pump is discharging into a pipe line, the pressure variation caused by any given plunger is approximately proportional to the velocity of the liquid being moved by that plunger. Thus, if degrees of crankshaft rotation were plotted against plunger velocity, the resulting curve is an approximate representative of the pressure variation existing during the pumping operation. With pumps of the double acting triplex type, such as employed herein, the plunger rods-11, 12, 13, etc., of a given pump go from zero to maximum velocity and back to zero during 180 of rotation of the respective crankshafts while making the discharge stroke. Thus, the liquid moved has the same velocity variation. The net effect of the six pumping chambersemployed in each double-acting triplex pump herein considered produces a fluid velocity variation which varies regularly but with sharp surge peaks at widely spaced intervals. Thus, if four such pumps are operating in step, i.e., each time a forward stroke is completed on one pump a forward stroke is completed on each other pump, the fluid discharged into the common manifold will exhibit unusually high velocity peak pulses at infrequent intervals. As will be readily understood, these pulsations set up vibrations in the pipe line and adjacent structures.

On the other hand, if the four pumps were operated out of step with the proper phase distinction between the movement of each pump crank shaft, the average velocity of the fluid distribution from all of the pumps would approximate a curve having a lower over all amplitude with the pump discharge peaks being of very small magnitude and positioned much closer together whereby the overall fluid distribution curve would follow a symmetrical pattern having slight deviations from the normal. As will be obvious, this type of operation provides a much better theoretical fluid distribution than can be obtained with an in-step operation and heavy surges are eliminated resulting in a substantially vibrationless fluid flow.

In order to obtain this condition, it is only necessary to so operate the four pumps as to obtain a 30 phase angle differential between the forward strokes of the respective pump actuator rods. In this connection, it will be understood, that the crank arms 21, 22, and 23 on the crank shaft 25, as well as the remaining crank armson the remaining crank shafts, are displaced 120 apart whereby the initiation or completion of the forward stroke for each pump chamber occurs in a precise timed relationship for constant crankshaft speed. Thus, considering the forward stroke of actuator 11 for pump as occurring at zero degrees of crankshaft rotation, 30 subsequently an actuator rod on the adjacent pump 50 begins its forward stroke. After 30 more rotation of the first crankshaft 25, i.e., after a total rotation of 60", anyone of the plunger rods on one of the remaining two pumps must start its forward stroke, and after 30 more rotation of crankshaft 25, i.e., a total rotation of any one of the plunger rods on the remaining pump must initiate its forward stroke. Thereafter, 30 more rotation of crankshaft 25, i.e., after a total rotation of a second actuator rod 12 of pump 10 is ready to initiate its forward stroke with an identical pattern being maintained throughout the next 120 of rotation with respect to the remaining pumps in the system, and similarly, for the third 120 of rotation. In this respect, it should be particularly noted that selection of the proper phase differential is calculated with respect to only the forward strokes of the respective actuator rods. This is necessary due to the fact that the maximum velocity of each stroke occurs before and after the mid-stroke. If a 30 phase angle differential was set up indiscriminately, or in a definite pattern of forward-back-forward, etc., the velocity amplitude of the fluid distribution curve would be greater and it would exhibit surge peaks at irregular intervals.

Since each of the pumps is driven by an identical synchronous electric motor connected to the pump, through identical gear trains, it is obvious that once the proper phase relationship is established between the respective pump crankshafts the relationship will be self-sustained until such time as one or more of the units is stopped and/ or restarted. This is due to the fact that synchronous motors operating in parallel will maintain a precise constant phase relationship with respect to the system to which all of the motors are common.

Various attempts directed to establishing a proper phase differential between the pumps of the system at the time of starting the units proved unsuccessful. It was discovered, however, that the synchronous motors could be momentarily slowed down while the rotating direct current field coils of the motor slipped with respect to the revolving magnetic field set up by the stationary A.C. windings with which the direct current field coils were normally locked at synchronous speeds. Conveniently, this slowing down can be accomplished by interrupting the direct current to the field coils of the motor for a short time interval when the motor is operating at partial load to cause slippage between the AC. and D.C. poles without incurring damage to either the electrical or mechanical components of the drive arrangement. The amount of angular slip with respect to synchronous speed is roughly proportional to the period of time that the D.C. field is interrupted, advantageously rendering the use of a conventional timer in energizing the interrupting relay practical and efficient. With motors of the size herein considered, i.e., having 22 poles and rated at 500 horsepower, an interruption of the D.C. field for about 1 and /2 seconds causes the motor to slow down or slip the angular distance represented by one pair of field poles. Since there are twenty-two poles in the motor construction, the two pole slippage is equivalent to 2 360 or an angular shift of 32.73" of the motor shaft with respect to anyother motor shaft operating from the same system at synchronous speed. A three second interruption causes a slippage of four poles and a four and one-half to five second interruption will generally produce a slippage of six poles. However, with larger slippages accurate control is seldom obtainable and it is preferred to limit the pole slippage to either two or four poles at a time, the nature of the equipment being such that the slippage is always an even number of poles or pole pairs. In view of the fact that the motor is geared to the pump crank shaft in the conventional manner by reduction gearing, the angular slippage of the motor shaft can be translated into a much smaller angular slippage of the pump crankshaft. In the specific example herein considered, the slippage of the motor shaft is 32.73 which through gears 26, 27 reduces to a crankshaft slippage of 4.22 Since the change in angular phase relationship of one pump crankshaft with respect to another can be obtained in such small increments, it is obvious that precise control can be exercised and the relative angular phase relationship between the respective pump crankshafts positively shifted as desired.

A limiting condition, however, is the maintenance of a proper load on the motors during the slipping operation. With the motor driving a normal full load, interruption of the energization of the field coils results in an unpredictable slip of large magnitude, whereas interruption of the energization of the field coiis at no or very low load results in no pole slippage due to the residual magnetism in the direct current field of the motor, which allows it to continue to operate at synchronous speed under this condition. It was established that satisfactory performance could be obtained for the purpose herein intended by reducing the load on each synchronous motor through the medium of reducing the pump discharge pressure to between 60% and 30% of normal.

Since the starting equipment of large synchronous motors of the type employed herein usually includes a polarized field frequency relay, it was found possible to provide an added coil 33, on this relay which would open its contacts in the coil circuit of the field application relay whereby the energization of the D.C. field coils could be interrupted for a predetermined period of time dependent upon the period of energization of the added relay coil. Advantageously, the added coil is energized through a timer having prescttable means for limiting the period that the DC. field is deenerigized.

The operation and function of the invention will be more readily understood by reference to Figs. 1 and 2 of the drawings illustrating the system as applied to four pumps. As shown, the synchronous motor 36 is adapted to drive shaft 23 and through geanings 26, 27 to rotate the pump crankshaft 25 at a constant speed, it being understood that the motors 76?, iii) and 15% perform an identical function. The energization of the motor 30 is obtained in a conventional manner by suitable manipulation of a standard starter unit consisting of closing switch 32 opening switch 32A, resistor 32C, solenoid winding 33, rod 34, .3 pole switch 35, switch 36, solenoid windings 4-9 and 49A and choke coil 49C connected between motor 3!) and. the three-phase generating system P by wires 29 and 44'. As will be readily understood by those skilled in the art, windings 49, deA are adapted to delay energization of the DC. field winding 31 by holding switch 36 open, which causes field application relay coil 33 to be -maintained de-energized and switch 32 to be maintained open until the revolving D.C. field of the motor approaches synchronous speed and the. phase position is proper for application of the field. The energization of the windings 49 and 49A from the alternating voltage induced in the DC. field windinr as previously indicated, serves to operate rod 37 against the force of a tension spring 37A to open switch 36 and de-energize coil 33 which in turn opens switch 32 to de-energize the DC. field 31. When the rotating D.C. field 31 of the motor ap proaches synchronous speed, winding 49A becomes nearly de-energized and as the voltage across Winding 4-53 passes through zero, spring 37A retracts rod 37 to close switch 35, energizing coil 33 which closes switch 32 thereby applying D.C. to the DC. field and opening switch 32A, opening field discharge resistor 32C, the motor thereafter operating at a constant synchronous speed. The same mode of starting is applicable to each of the remaining motors 70, 110 and 156, out as heretofore indicated, the relative phase relationships between the respective motors and therefore between the respective pumps driven thereby, will be unpredictable and in many instances will be such as to lock two or more of the pump actuator rods in step, i.e., in synchronism, it being understood that the electrical characteristics of synchronous motors, when connected to a common generating system, serves to retain the motors in the precise angular electrical and physical phase relationship which existed upon starting. In such event, the in-stepor synchronous operation of two or more of the pumps produces large amplitude surges in the velocity of the fluid distributed to the common manifold of the system, and if allowed to remain unmodified, will set up destructive vibrations in adjacent structures.

In accordance with the present invention, this in-step or synchronous condition can be readily and simply modified in such manner as to orient the respective motors of the system and therewith the respective driven pump members into a predetermined desynchronized relationship so as to obtain a substantially constant velocity in the fluid distribution. This conditioning of the system for vibrationless operation is obtained via the pushbutton switch 4-5 of the motor control circuit 39, in the following manner.

With each of the synchronous motors 36, 7t Elli), and energized and rotating the pump crankshafts in a random but locked phase relationship, each of the supervisory control units A, B, C and D of circuit 171 is serially connected with the flasher unit 189 of reference circuit 190 by actuation of the respective switches 5.72. As heretofore indicated, this results in the completion of a series circuit from the energy source of network 171 through the flasher unit I each time the make and break units 179, 174 of the respective control units A, B, C and D mate. It thus will be understood that light 18% is caused to flash three times for each revolution of each crankshaft as each crank arm moves its connected actuator rod to complete the forward stroke.

This periodic flashing of unit 18d is availed of in connection with the reference disc to visually indicate the synchronous or non-synchronous condition existing between the respective pumps of the system as follows. As heretofore indicated, motor 186 is adapted to drive disc 188 through gear train 137 at such speed that the disc makes three revolutions for each crankshaft revolution, it being recalled that the synchronous motors for each pumping unit operate at synchronous speed and thereby rotate each of the pump crankshafts at the same speed. Disc 188 is provided with the single radial line 189 and when light from flasher unit 13% is beamed upon the face of the disc, the frequency of the light flashes in relationship to the speed of disc 13!; is such that the radial line 189 appears to stand still. Considering the stroboscopic appearance of the disc with only the pump 10 and control unit A connected in the system, it will be appreciated that as each actuator rod 11, 12, and 13 completes its forward stroke, light tee is energized to initiate a brief but brilliant flash. However, during the precisely identical time interval that each flash occurs, a motor 186 rotates disc 183 three complete revolutions so that the illumination of radial line 189 with each flash portrays the radial line in the same physical position, as if it were standing still.

If a second pump is energized with its contactor unit connected in circuit 170, as for example pump 51 and contactor unit B, the corresponding periodic energization of flasher unit 18% will reveal the radial line 139 in some other angular position, unless it happens that the two pumps are operating in step, and the disc when viewed visually will appear to bear two radial lines. If the two pumps are operating in step, i.e., synchronously, the contactors A and B will be completing the light flashing circuit simultaneously and only one radial line will be viewed visually. Thus, if the four pumps are operating and all four contacting units are connected in circuit, four radial lines will appear on the face of disc 188 unless, again, two or more of the pumps are operating in step.

Previously, it has been brought out that the ideal fluid distribution curve will be attained for a pumping system utilizing four double acting triplex pumps, as herein, when there is a 30 angular phase differential between the various pump crankshafts. If pumps 16 and 56, heretofore considered to be energized simultaneously, have this relationship, the relative position of the radial 7 lines as :stroboscopically portrayed on the revolving disc will be spaced apart by an interval corresponding to a I time phase differential of 30 of crankshaft rotation. Since the disc 188 revolves three times as fast as the respective crankshafts, the radial lines will appear to be three times 30, or 90 apart. As will be apparent to those skilled in the art, if the ideal desynchronized condition exists, four radial lines, corresponding respectively to the relative angular positions of the four pump crankshafts, will appear on the face of disc 90 apart, and will form a cross as shown by the dashed lines 195 in Fig. 2. Although this description has been made with reference to the operation of four pumps by four synchronized motors, it will be readily appreciated that the same control arrangement may be employed when three pumps, or five pumps, or more are operated. With three pumps, the phase differential between respective pump crankshafts should be 40 and the angular spacing between the radial lines appearing on the face of disc 188 becomes 120. With five pumps in the system, the angular spacing on disc 188 between the respective radial lines would be 72 for the ideal desynchronized condition.

From the above it will be apparent that a single operator can very readily reduce the pressure load on a given pump and manipulate the push button unit 45 in the control circuit of the respective motors to change the angular phase relationship of each in the manner previously described. Thus, the operator upon starting the system will view reference disc 188 to ascertain the existence or nonexistence of a synchronized condition and by selective depression of the manual push button 45 cause a predetermined pole slippage in the connected motor to shift the existing angular phase relationship between that motor and the remaining motors of the system, the new phase relationship being instantly shown by the relative position of the radial lines appearing on the face of disc 188. As heretofore indicated, the amount of pole slippage desired is governed by the setting of valve 48 in the dash pot unit 47 connected to the manually operable switch 45 whereby in the event a single pump, such as .10, is the only component out of the desired ideal desynchronized relationship, the desired relationship may be attained by a single depression of switch 45. In order to simplify the operation of desynchronizing the motors, a scale 183 is placed in back of rotating reference disc 188 and is calibrated to show the angular increments corresponding to the slippage of one pair of poles. In the instant example, this increment is three times the two pole crankshaft slippage figure, previously shown to be 422, and the calibration marks on the disc are spaced three times 4.22", or 12.66 apart.

In order to prevent inadvertent damage to the motor circuit, as for example, in the event the operator attempts to slip motor poles without reducing the load on the motor by reducing the pump pressure, control circuit 39 is provided with the safety switch 40 which, as previously described, is normally closed but is adapted to be opened upon the energization of a current sensitive solenoid winding 42 connected in one of the three phase power leads 44. With a reduced load on the motor the amperage in lead 44 is low and the current sensitive relay will close its contacts making it possible for the switch 45 to control circuit 39 and selectively deenergize the motor D.C. field to cause a predetermined pole slippage and angular phase shift. With a higher load on the motor, as for example, when the pump is operating at full normal pressure, the motor current is increased proportionately and the amperage in coil 42 is sufficient to retract switch 40 and open circuit 39.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope hereof, it is to be understood that the invention is not limited to the specific embodiments hereof, except as defined in the appended claims.

What is claimed is:

1. A system for desynchronizing elements driven by synchronous electric motors comprising a plurality of driven elements, angular phase indicating means connected to each of said elements to indicate their respective phase relationship, a plurality of synchronous motors including stationary A.C. armature windings and rotating D.C. field windings, coupling means operatively connecting said motors to respectively drive said elements, means connecting said A.C. armature windings of each of said motors to a common A.C. source of electrical energy, a motor control circuit energized from said common source of A.C. electrical energy and including a switch in the DC. field circuit of each of said motors, said switch connecting each of said D.C. field windings to a source of DC. electrical energy, a relay connected to open said switch upon energization of said relay, and manually operable control means in said motor control circuit including structure for selectively energizing said relay for a predetermined period of time to cause slippage between the revolving magnetic field set up by the stationary A.C. armature windings and the rotating D.C. field windings of the motors to shift the angular phase relationships between said elements whereby said elements can be desynchronized in cooperation with observation of said phase relationships upon said display means to minimize vibration inducing pulsations.

2. A system as set forth in claim 1 wherein said angular phase indicating means is comprised of a supervisory circuit having a connection to said common source of A.C. electrical energy, said supervisory circuit further including make and break contactor means connected to be operated in timed phase relationship with each said element and including structure for periodically energizing said supervisory circuit each time a particular element assumes a predetermined phase relationship, a light flasher unit connected to said supervisory circuit and adapted to be energized to emit illumination each time one of said make and break contactors completes said circuit, a reference network associated with said flasher unit and including a synchronous motor connected to said common source of A.C. electrical energy and connected to drive a reference disc bearing a single radial line at a speed so synchronized with the speed of said elements as to complete a single revolution of said disc for each cycle of any element whereby the relative angular phase relationships of said elements can be visually portrayed stroboscopically on said reference disc to obtain an instantaneous indication of the existing phase relationships between said elements.

References Cited in the file of this patent UNITED STATES PATENTS Re. 21,629 Shutt NOV. 19, 1940 2,175,923 Shutt Oct. 10, 1939 2,239,244 Nelson Apr. 22, 1941 2,528,131 Garretson Oct. 31, 1950 

